Abstract

There is a recent interest in nanoscale materials, in particular, nanotubes based not only on carbon. In this study, photoemissionspectra of single nanotubes deposited on a Si surface were recorded in order to explain their electronic structure. The photoelectrons were excited by a femtosecond laser oscillator resulting in two-photon photoemission. A spectromicroscopic technique based on imaging time-of-flight detection was used to record the spatially resolved photoelectron spectra. Self-consistent electronic structure calculations for slabs using the full potential linear augmented plane wave method are used to explain the peculiarities of the observed spectra. It turns out that the nanotubes are semiconducting with a band gap of about . The two-photon transitions proceed through intermediate states in a region with high density of states; this gives rise to a high photoemission intensity.